Electrostatic discharge device

ABSTRACT

A device which enables the user to dissipate an electrostatic charge, such as is picked up from walking on a rug, by controlling the rate of discharge through a resistor which is mounted within the device, and the device is worn on the user&#39;&#39;s finger as a ring and which is thus kept conveniently available, and the device incorporates an indicator lamp which gives a visual indication of the charge dissipation.

Umted States Patent 1191 [111 3,745,412 Ruff 1451 July 10, 1973 [54]ELECTROSTATIC DISCHARGE DEVICE 390,115 9/1888 Delany .L 174/5 R [76]Inventor: John Denis Ruff, 206 Birch St.,

Alexandria, Va Primary Examiner-L. T. Hut

[221 Filed: Nov. 19, 1971 [57] ABSTRACT [211 App! 200527 A device whichenables the user to dissipate an electroy static charge, such as ispicked up from walking on a [52] US. C1 317/2 R, 317/2 B g, ycontrolling the rat of discharge through a resiss 1 1m. (:1. 1105i 3/00tor which is mounted i in h i n h vi e [58] Field of Search 317 2 R, 2B, 2 D is worn on the ussrs finger as a ring and which is thus keptconveniently available, and the device incorpo- [56] R f r Cit d ratesan indicator lamp which gives a visual indication UNITED STATES PATENTSOf the Chfll'gC dissipation.

3,099,774 7/1963 Crane 317/2 D 1 Claim, 6 Drawing Figures PATENIEU 73 I2 38 I M I 6157 h l FIG.4

FIG.5

ELECTROSTATIC DISCHARGE DEVICE Often during winter months, when the airis very dry, many people have problems with static electricity. Peoplewalking on rugs, sliding on fabric furniture, sliding on vinyl seats incars (and on vinyl furniture) tend to generate substantial staticcharges. Then when they touch their hands on a conductor surface thischarge is conducted away with a momentary electrical current of highintensity. The result is a painful shock. My invention uses a resistorto control the discharge current flow so that while the same electricalcharge is dissipated, the rate of discharge (that is, the current level)is reduced to a level which is not painful. This is possible because thepain of electric shock depends on the current level flowing through thebody tissues. If the current level is reduced enough, no pain is felt.In my invention the resistor is mounted in a ring to be worn on theusers finger. This places the device in a convenient position so thatthe user can reach out and touch the device to a conductor surface andthus be rid of the bothersome charge with the minimum of trouble.

In use, a person walking on a rug would know that he had accumulated astatic charge. Then as he approached a door he would expect that if hetouched the doorknob he would get a shock. But with my invention hewould only have to touch the ring to the doorknob first to discharge hisstatic charge and then go ahead and open the door. He would not get ashock at any time. An insulated electrode surface faces outwards fromthe ring so that a contact can be made easily by this surface with theconducting surface. The electrode surface is connected electrically toone side of the resistor, while the other side of the resistor makeselectrical contact with the wearers finger.

An additional feature is the use of a small glow lamp which is builtinto the ring and which is wired in series with the resistor. While thestatic charge is being discharged through the resistor this lamp lightsand provides a visual indication that discharge is taking place.

The user then knows that he has made proper contact with the conductingsurface.

In the drawings:

FIG. I gives a general descriptive view of the device.

FIG. 2 shows the operation during discharge.

FIG. 3 shows the device incorporating an indicator lamp.

FIG. 4 shows an alternate type of indicator lamp.

FIG. 5 shows an alternate construction of the device using a one-pieceplastic body.

FIG. 6 shows an alternate construction of the device using an all metalconstruction with an insulating liner.

DESCRIPTION FIG. I shows the users hand 2 and assuming that the user hasbeen engaged in activity causing him to be charged with staticelectricity, and that hand 2 (and finger 3) then carries a positivestatic charge. The doorknob 4 is then negatively charged (relative tothe positive charge of the user). A metal band 5 fits on finger 3.Attached to band 5 is an insulating plastic housing 6. Mounted withinthis housing is resistor 7 with its electrical connection points 7a and7b. Point 7a is connected electrically to band 5 at lug 5a which is aprotruding part of band 5. On the side of housing 6 that is facingoutward from finger 3 is mounted an electrode 8. Resistor connectionpoint 7b is connected electrically to this electrode.

OPERATION Without the benefit of my invention if finger 3 (FIG. 1) weremoved close to doorknob 4, at point 9, a spark would occur and the userwould experience a painful shock as a momentary intense current flowdischarges his bodys static charge through the spark at point 9. Thestatic potential involved is generally some thousands of volts, and whenpoint 9 is close enough to the doorknob, dielectric breakdown of theseparating air occurs and an arc is established. This are offers verylittle resistance to the flow of current between the finger and thedoorknob, and so with the high voltage involved, a very high currentthen flows. And since the painful effect of electric current relatesprimarily to the intensity of the current, the current flow throughpoint 9 is quite painful. Fortunately, however, the bodys static charge(though high in voltage) is limited in capacity; so that when the arc isestablished, the charge is dissipated instantaneously, and the currentflow (through the arc) ceases. But to prevent the are at point 9, finger3 must not be placed close enough to the doorknob 4 to allow an arc,until the user s body charge has been dissipated.

CHARGE DISSIPATION With the users body carrying a static charge (asshown in F101) and assuming a potential of 3,000 volts; then thisvoltage drop will be present across the air space between electrode 8and point 10 on the metal door-plate 11, with electrode 8 being positiveand door-plate 11 negative (relatively). Then, as shown in FIG.2, whenelectrode 8 is moved close enough to point 10, an are 12 is established.Electrode 8 and resistor connection 7b then become negative, relative tofinger 3 (and to resistor connection 7a which is connected electricallyto finger 3). This places the voltage drop across resistor 7, andassuming a value of 3 meg-ohm for resistor 7 the current flow can not begreater than 1 milliampere, which is not painful to the user. Are 12does have some resistance to current flow but it is not significant whencompared to resistor 7. Are 12 may collapse before all of the users bodycharge is dissipated, but the user continues to close the gap betweenelectrode 8 and plate 11 until direct contact is made and then all ofthe charge will be dissipated. The time taken for total dissipationthrough resistor 7 is much greater than when the charge is dissipatedthrough the are at point 9 (FIG.1) and variations in conditions causesome variations in this time. Never the less tests have shown thatacceptable discharge can generally be achieved in less than one tenth ofa second. The size of 3 meg-ohm for resistor 7 can be reducedconsiderably, and satisfactory results still maintained, particularlywhen static charges of lower potential are encountered. Howeverresistances less than 20,000 ohm have been found to be generallyunsatisfactory. Band 5 can be a solid band as shown in FIG.1, or, it canbe split as shown at 5b (FIG.2) to allow adjustments for various fingersizes to be made by bending of the metal band.

INDICATOR LAMP FIG.3 shows an arrangement using indicator lamp 13 toindicate discharge current. This lamp is of the type generally called aglow lamp and which consists of two separated electrodes mounted in atransparent envelope filled with a gas having a low dielectric strength(such as neon, argon, etc.). This lamp 13 is shown connected in serieswith electrode 8 and resistor 7. Alternately the lamp could be connected(electrically) between resistor 7 and metal lug 5a. A characteristic ofthese glow lamps is a 90 volt (approx.) starting voltage so that withthe high static voltages involved, the lamp will always start. Theirresistance to current flow is small compared to resistor 7, so that theresulting current flow when lamp 13 is connected in series with resistor7 to a 3,000 volt static charge will still be about 1 milliampere.Typical small types of glow lamps are rated at one twenty-fifth watt andrequire less than 1 milliampere to light them; so that these types givea good indication of current flow during charge dissipation. In use theindicator lamp enables the user to be sure that he has properlydissipated the static charge before making solid contact between hishand and the conductor surface (doorknob etc.). When an indicator lampis used, housing 6 should be made of transparent material or,alternately, an opaque material used, but with an opening 14 in thehousing (FIG.3) so that the lamp 13 can be seen.

An alternate type of lamp known as a Light Emitting Diode (LED) has lowcurrent requirements and fast response, and can be used in place of theglow lamp l3. FIG.4 shows LED used in a similar manner to that alreadydescribed for glow lamp 13. LED 15 can be placed so that it is visiblethrough opening 14 in a similar manner shown with lamp 13 in FIG.3, orit can be mounted so that its light emitting surface 15a (FIGA)protrudes outside housing 6 through opening 14. With some LEDapplications a small capacitor 16 can be used (as shown in FIGA) toprotect the LED from high voltage breakdown.

FlG.5 shows an alternate method of constructing the device. The band 5and housing 6 as shown in FIGS.1,2,3,4 are now replaced by a singlepiece of plastic 17 and electrical contact is made with the finger by aninserted metal piece 18 which is connected electrically to resistor 7.The operation is otherwise as already described. This type ofconstruction can be used with the arrangement using resistor 7 only, asshown in FIGS.1,2. Or, it can be used with the combined resistor andeither type of lamp as shown in FIGS.3,4,5.

FIG. 6 shows another alternate method of constructing the device. Band 5and housing 6 are replaced by a single metal piece 19 which has aninsulating liner 20 which prevents any unwanted electrical contact (orarcing) between the housing portion of metal piece 19 and electrode 8,or other electrical components. Contact is made between metal piece 19and resistor 7 at point 21. The operation is otherwise as alreadydescribed. This type of construction can be used with the arrangementusing resistor 7 only, as shown in FIGS.1,2. Or, it can be used with thecombined resistor and either type of lamp as shown in FIGS.3,4,6.

I claim:

1. A static electricity discharge device combining an electricalresistor which has two points of electrical connection to it and meansof mechanically attaching the said resistor to a persons finger so thatthe said resistor and the said means of attaching form a unit which canbe worn in the manner of a jewellery ring and the said means ofattaching including an insulated plastic housing in which the saidresistor is secured and means of making an electrical connection betweenone of the said two points of electrical connection and the said finger,and an electrode which is electrically connected to the other of thesaid two points of electrical connection, and the said electrode isinsulated electrically from the said means of making an electricalconnection, and the said electrode is mounted on the said plastichousing and facing away from the said finger and positioned so that thesaid person can extend thevsaid finger toward an electrical conductorsurface and cause the said electrode to make electrical contact withthis surface thus discharging the said persons electrostatic chargethrough the said resistor at a controlled rate, and also mounted withinthe said plastic housing a lamp means of indicating flow of electricalcurrent through the said resistor and the said lamp means beingconnected electrically in series with the said resistor.

1. A static electricity discharge device combining an electricalresistor which has two points of electrical connection to it and meansof mechanically attaching the said resistor to a persons finger so thatthe said resistor and the said means of attaching form a unit which canbe worn in the manner of a jewellery ring and the said means ofattaching including an insulated plastic housing in which the saidresistor is secured and means of making an electrical connection betweenone of the said two points of electrical connection and the said finger,and an electrode which is electrically connected to the other of thesaid two points of electrical connection, and the said electrode isinsulated electrically from the said means of making an electricalconnection, and the said electrode is mounted on the said plastichousing and facing away from the said finger and positioned so that thesaid person can extend the said finger toward an electrical conductorsurface and cause the said electrode to make electrical contact withthis surface thus discharging the said persons electrostatic chargethrough the said resistor at a controlled rate, and also mounted withinthe said plastic housing a lamp means of indicating flow of electricalcurrent through the said resistor and the said lamp means beingconnected electrically in series with the said resistor.